Closed feed system for steam power plants



H. HILL'IER March ,13, 1945.

CLOSED FEED SYSTEM FOR STEAM POWER-PLANTS Filed Feb. 27, 1943 4 Sheets-Sheet l o o o oo o o o oo oo o 0 O O O 0 0 0 0 0 oo n."o o ooooo o ooooooo oooooooooooow o ooooooooooooooooo ooo oooo oooooooooooo Ooo FIG.

am am f March 13, 1945. H; HIL-LIER 2,371,443

, CLOSED FEED SYSTEM FOR STEAM POWER PLANTS March 13, 1945.

CLOSED FEED SYSTEM FOR STEAM POWER PLANTS Filed Feb. 27, 1943 4 Sheets-Sheet 5 l I F |52 64 Y56 L E 5^ .l P55 ql-wu. M

H. HILLIER March 1 3, l1945.

CLOSED FEED SYSTEM FOR STEAM POWER PLANTS 4 Sheets-sheet 4 wail Filed Feb. 27, 1943 Patented Mar. 13, 1945 CLOSED FEED SYSTEM Fo-R s'rEAMPoWER 1 "PLANTS, o.

l Af 2,371,443A

Harold Hillier, Glasgow, scotland, "assigno'r to"y G. & J. Weir, Limited, Glasgow, Scotland, 'a corporation of Great Britain Apolioanon Fobroary 21, 1943,y soriai No. 477,367 In Great Britain March u2, 1942 s oioims. (cl. ice- 451) The present invention relates to closed feed systems for steam power plants operating in parallel and each including a steam generator, a steam turbine, a steam condenser, and the appertaning feed water and steam connections.

The object of the invention is to provide a simplified arrangement whereby two or more closed feed systems can be operated stably. and satisfactorily in parallel and wherebyiany external feed tanks can, if desired, be dispensed with.v l

According to the invention there is provided a well at, and in, or connected to, the bottom of each condenser, the water capacity of such well being sufcient to accommodate, between the minimum water level required by the condensate extraction pump and preferably the bottom tubes of the condenser, the volume of feed water returned from the boiler or boilers associated with and proportional to that condenser, there being.

associated with said condenser wells means whereby differences between the return of water to the respective condensers, variations in the operation of the respective condensers, their associated condensate extraction pumps, and differences in the characteristics of such pumps are automatically adjusted so as to ensure stable and satisfactory parallel operation of two or more closed feed systems. E

The elimination of external feed tanks ensures that the feed water never leaves the closed feed system and has, therefore, no 4opportunity to absorb the component gases of atmosphericair the oxygen of which has a particularly deleterious effect on steel parts of the system. The continual circulation of the working iiuid throughthe condenser ensures the optimum degree of removal of all non-condensable gases. Further' advantages obtained by the omission of an external feed tank are saving in weight and space and the re`` duction of free water in the system to a. minimum.

condensers, differences in the condenser loadings n and differences in the characteristics of the various condensate extraction pumps, Furtherras Will loe-explained later, satisfactory parallel operation of the various condensate-extraction pumps is ensured at all loadsand under al1..conditions likely toobtain. i

:,The invention will nowbe described with referencev to the; accompanying. drawings in which:

Fig. ly showsra section through a condenser Fig. 3 shows in ,section oneform of appal ratus lfor automatically,'controlling .theiiow of .feedwater to and fromV a condenser `in accordancev witntno invention. f. y

,.Figl 4 is a diagram illustrating the kparallel operation of closed feedsystem units in accordance with the invention, e g, Referring to Fig. 1, the condenser shell I 4is providedl with` a welll thecapacity of which `is sufficient to accommodatethe, changes in water level which occurfin the voperation of a steam power plant vwith a closed feedsystem. Steam generators in operation have a greater Vweight of water in the generator at Vno load than .whenl steaming., due tov the yvolume of the steam .bubbles below `the generator water level as such. steam bubbles are formed and rise to the Waterlevel. This volumeof steam bubbles increases Withy boiler load to afmaximumat the maxium .generator load with the consequence thatthe `weight of water in the generator falls as the generatorload is increased and the weight vof water so displacedmust be accommodated in thecondenser well 2.

The condenser well is so proportioned that this volume of` water isaccommodated between the water level required for the satisfactory operation of' thecondensate extraction pump and a water level suiciently below the bottoml row of tubes in the-condenser to permit a flow of steamacross the water level to ensure, thesatisfactory 'des aerationof all condensate Vfalling into the well.` 1 ,The Well is providedwith `an outlet 3 from which thecondensate extraction pump withdraws condensate'from thek condenser.

The level A-A indicates the minimum water level necessary to cause the' flowI of condensate through `the outlet 3k and give ahead sufficient to ensure the satisfactory operation of ther-ondensate pump. To-.provide a ymargin to meet variations in operation, ithe normal water` level with'rno loadon the-'boiler :is-arranged at some suitably higher level: such. as'Bl-Bi" lAs the boiler load isincreased, the water displaced in the boiler by the formation of steam bubbles is accommodated in the condenser well until, at full power, the Water level rises to C-C which is suflciently below the bottom row of tubes in the condenser to allow steam to pass from the steam inlet 4 of the condenser down the steam lane 5 to the surface of the water in the well 2, so that all condensate falling from the condenser tubes into the well must pass through such steam and, in doing so, be heated to boiling point so that it is at the maximum possible temperature before leaving the condenser, and all gases are driven out of the condensate before it passes into the feed system.

D-D shows the minimum water level which it is permissible to carry with full power on the boiler, the volume of water between the levels C-C and D-D being equal to the volume of water between the levels B-B and A-A. If the water level is being carried at D-D with full power on the boiler and the boiler load is reduced to zero, the water between the levels D-D and A-A will be discharged into the boiler to maintain the level in the boiler at the required height.

In Fig. 2 are shown two steam power plants,

' similar units in each plant being denoted by the same reference numerals. The steam turbine 6 receives steam from a steam generator 'or boiler I and exhausts into a condenser 8 which is provided with a well 9 below the bottom row of condenser tubes.

Ill withdraws condensate as required from the condenser well 9 and discharges the condensate into the feed system through the non-return valve II. Air and other non-condensable gases are withdrawn from the condenser 8 through the pipes I2 by the air ejector I3 and discharged with the air ejector operatingsteain into the ejector condenser I4 wherein the steam is condensed and the heat transferred to the feed water which is discharged through the ejector condenser by the condensate extraction pump I0, the condensed ejector steam being drained into the condenser through a trap I and the pipe IB. After The condenser well S has a water capacity lwhich is greater than the difference in the weight of water in the boiler 'I between no boiler load and maximum boiler load, and such capacity is available between the minimum water level required by the condensate extraction pump and the bottom row of the tubes in the condenser.

' When the two boilers l are being operated in parallel, which is the most convenient method of operation, it is necessary to ensure that the Vweight of water displaced from the boilers A condensate extraction pump as the load increases from no load to full load shall be accommodated equally between the two condenser wells 9, and means must be provided to ensure such satisfactory distribution of the feed water between the two condensers irrespective of variations in the vacua in the condensers 8, the diiferences in loadings of the condensers and differences in the characteristics of the condensate extraction pumps Il). For this purpose, I providefor each'condenser a closed feed control valve comprising an overflow and an inlet valve controlled by a float which is actuated from the water level in the condenser well 9. In Fig. 2 Irhave shown a separate chamber 28 connected to each condenser by pipes 29 and 30, `so that the waterk level prevailing in the float chamber 28 is substantially the same at all times as the water level prevailingr in the condenser well.9. The float 3l rises and falls in the float chamber 28 with the rise and fall of the water level and in so doing actuates the overflow valve 32 and the inlet valve 33. The float chamber is so placed relatively to the condenser well 9 that, on a change of water level upwards from a predetermined level, the overow valve 32 is opened to effect the removal of water from the associated condenser by Way of the condensate extraction pump I0, discharge line 34, overflow valve 32 and w pipe 35, from where it can iiow to the inlet valve leaving the ejector condenser, the feed -water l passes to the suction of the boiler feed pump I8 which discharges the feed water through the drain cooler I'I and feed heaters I9 and 2D to the boiler feed regulator 2|- which controls the flow of feed water intothe boiler 'I as necessary to maintain the water level in the boiler to correspond to the boiler load requirements. The feed heaters I9 and 2D are supplied with heating steam bled from the main turbine 6 through pipes 22 and 23, respectively, the resultant drainage in the heater 20 being led into the heater I9 by the pipe 24 and the combined drainage from the heater I9 passing into the drain cooler I'I through the pipe 25. An evaporator 26 is supplied with bled steam from the main turbine 6 through the pipe 22 and such steam is used to evaporate sea water or other crude water in the evaporator, the vapour thus produced being condensed in the drain cooler I1 into which the evaporator coil drain is also led, the resultant drainage passing to the condenser 8 by the connection 21. Y f Y It will be seen that all steam used in the power plant and its associated feedheating and evaporating plant is condensed-and drained into the condenser well so that the main circuit and the sub-,circuits are all totally enclosed and at no time or place does the working fluid make any contact with the atmosphere.

33 on the other condenser and pipe 36 into that condenser; or, in the event of the inlet valve being closed, the overflow is discharged by way of a pipe 31 and the spring-loaded valve 38 to a reserve feed tank 39 through an open funnel 38A. The level at which the overflow valve opens is preferably the level C-C in Fig. l. The change of water level downwards from the predetermined water level, which is preferably C-C in Fig. 1, opens the inlet valve 33 to permit water to enter the associated condenser from the other condenser if the water level in that other condenser has risen above its predetermined operating water level.

It will be seen that, at full power, the wate level in the condensers should be maintained between the levels D-D and C-C, and if there is any tendency for the water level in one condenser to rise above the level C-C, ,the overflow valve on that condenser is openedand water is discharged into the other condenser, until the level in that condenser reaches the level C-C, in which case that inlet valve is closed by the operation of the float and the rise in Ypressure due to the closing of that inlet valvewill cause the pressure in the pipe line 3l to rise suiciently to lift the spring-loaded valve 38 and permit any excess water not required in they condensers to pass into the reserve feed tank 39.

If the distilled water producedV by the evaporating plant is in excess of requirements, the surplus will be discharged through the overflow valves, pipe 31, spring loaded valve 3B, and open funnel 38A to the reserve feed tank 39... The make-up to the system should, in general, be

operated so that Ithere is a slight"k continuous overflow to the reserve feed tank, `and the open funnel enables the operating personnel 'to verify visually that an overflow is being obtained.

I may arrange for'the reserve feed tank to` be connected to one or more of the condensers, such connections to be provided with a valve which may be manually operated so as to pass water, when required, from the reserve feed tank into the condenser or condensers. I may arrange for such connection to be automatically operated by a float which may be arranged in a chamber separate from the condenser but con;- nected thereto by pipes so that the level in the chamber is substantially te same as the level in the condenser.

. On one of the condensers in Fig. 2, I have shown such a float chamber 4I connected to the condenser by pipes 42 and 43 and provided with a float 44 which operates a valve 45 to control the ow of water from the reserve feed tank 39, by way of the pipe 40, into the condenser.

The float-operated valve 45 may beso arranged that it opens whenever the water level falls below some predetermined level in the condenser Well such as the level D--D, `in which case water can be drawn from the reserve feed tank into the condenser when so desired.

The connection 40 may be provided with a manually operated isolating valve 46 which can be opened'when it is desired to pass water from the reserve feed tank into the closed feed system.

The neat-operated valve 45 or the manually operated valve 46 maybe comparatively small in size and limited tosay, sufficient to provide an infiow of about per cent of the maximum rate of feed ow in the closed circuit.

It will .be understood that the overflow and inlet valves ,32 and 33 comprising the means for controlling the closed feed circuitin accordance with the invention can be comparatively small since they are required to deal only with differences in the operation betweenthe several condensers operating together and, for this purpose,

the size of the valves can be limited to that which will pass, say, about per cent of the maximum rate of feed flow through the closed through the valve spindle 55 on which are prov vided pistons 56 and 51, which guide the valve spindle, and pistons 58 and I59 which engage with valve seats 60 and 6I, respectively, to control the overflow and inlet of water from and `to the condenser respectively.

The extraction pump discharge is connected to the branch 62 to permit overflow water to be passed through the valve seat 60 under the control of the overow valve piston 58, water passing through the overflow valve, and leaving the valve body 52 by the branch 63. The branch 63 also permits inlet water to pass into the valve body 52 whence it can now through the inlet i valve seat 6I under the control of the inlet-valve piston 59 to the branch 64 whence the water can pass into the condenser with which the closed feed controller is associated. H i* To ensure that v`the leakages past the Apistons 56 and 51 do not buildup any pressure which is likely to disturb the hydraulic balance of the valve member, the chambers 65 and 66 associated with the pistons 56 and'l, respectively,

are coupled by a balance pipe 6l so that they pressure in the two chambers is substantially the same.

The positions of the overflow piston 58 and the inlet piston 59 relatively to their seats '60 and 6I, respectively, are such thatwhen 'the'.loatis position throughout the further downwards travel of the float 3l, which progressively opens the inlet valve 59 relatively to its seat 6I.

' I may arrange for a small travel of the ioat during which both the overflow valve 58 and the ldenser well without any-'pumping inlet valve 59 are closed in order to permit small uctuations in the quantity'of water in the conaction. taking place.

It will be seen that, whenever a condenser well reaches a predetermined level at which thefloat opens the overflow valve, the extraction pump associated 'with that condenser Iwell tandis charge water through the overliow lvalvey into a pipeline which is connected to the several branches 63 on the respective closed feedcontrollers on the other condensers.

If any condenser `has a Llow water level com-f pared with the predetermined overflow levelthe inlet valve on that condenser will be .open and water can pass into that condenser until the surplus water from thecondenserfwhich isonoveriiow has been transferred. il

It will be seen that any surplus Water in a condenser above the predetermined overflow level is transferred to one or other of the condensers in which'the water level is below the predetermined overflow level. In the event of all the l condensers in operation being full of water to the overflow level, thesurplus water is transferred through a spring-loaded valve to the reserve feed tank, as explained in relation to Fig. 2.

Fig. 4 is a diagram illustrating the parallel operation of the closed feed system units. For the sake of simplification, two-condensing systems only are illustrated. The line Y-E shows the discharge pressure capacity characteristic of a condensate pump Y. The line X-F shows the corresponding characteristic of a condensate pump X which is operating on the second condenser, the difference in characteristics being due to difference of vacua in the two condensers, or difference in operating speeds of the two condensate pumps, or differences inthe manufacture of the impellers ofthe two pumps. The combined characteristic of the two pumps X and Y is shown by the curve X-G-H. When the two pumps X and Y are operating in parallel, there will be a frictional drop between each pump and the common point of discharge, such frictional resistance being proportional to the square of the quantity of water flowing between the pump and the common point of discharge. At the combined discharge, the discharge pressure of both pumps is the same for both pumps, but the quantities of water discharged by the two pumps are diierent because of the different characteristics of the two pumps. Assume that the common discharge pressure is M, then the quantity of water discharged by the pump X is JL while LM is the quantity discharged by the pump Y and is equal to JK. If the two condensers are on equal loads, the condenser associated with the pump Y will fill up until the overflow valve is opened and pump Y discharges some of the condensate into the 'other condenser whence the pump X delivers it to the boilers. The quantity of condensate formed in the condenser with the pump Y is JK, which is equal to LM in the combined characteristic, and, of this quantity, MN is 'discharged to the system by the pump Y, while LN is discharged through the overflow valve where LN is equal to KL, and is subsequently discharged by the pump X to the system where JK is also equal to the condensate formed in the condenser with the pump X. If the other condenser is also full to overow level, the quantity LN will be discharged to the reserve feed tank. This transfer of water will take place continually and adjust automatically at all times any dilerences between the condenser vacua, pump characteristics and any factors which affect the pum characteristics.

It will be appreciated that all the water required by the boilers during any iluctuations of load between full power and no load is available in the wells in the bases of the condensers, and no external source of water need be provided.

Since the whole of the working fluid is within the main circuit or sub-circuits connected to the main circuit, contamination from the atmosphere is prevented, and any deleterious gases which may enter the system in such parts of the system where a vacuum exists are removed by the vacuum-producing apparatus of the condensers, the condensers being designed to give the maximum deaerating effect so that the water discharged from the condensers into the feed circuit isvat'the maximum possible temperature with the consequent optimum thermal efficiency and is free from any gases which might have corrosive effects on the parts of the steam power plant.

With a plurality of condensers in operation, any maldistribution of water between the condensers due to variations in loads is automatically adjusted by the operation of the closed feed controllers associated with the condensers.

What is claimed is:

1. A closed feed system for steam power plants operating in parallel, including at least two condensers having wells in their bases, condensate extraction pumps connected to said wells, water level controllers associated with said condenser wells and each comprising an overow valve, an inlet valve and a float operative on change in water level in the respective condenser well to open the overflow valve when the water level in said well rises above a predetermined level and to open the inlet valve when the water level falls below a predetermined level, piping connecting said valves and extraction pumps whereby condensate passing from one condenser through the overflow valve of the respective condenser when open may pass through an inlet valve which may be open of another condenser, a reserve feed tank, a connection between said piping and said feed tank whereby condensate which passes through the overow valve of one condenser when the inlet valve of no other condenser is open may pass to said reserve feed tank, and a springloaded valve intercalated in said connection.

2. A closed feed system for steam power plants as claimed in claim l, including an evaporator intercalated in the system to makeup water losses from the system and connections including said spring-loaded valve for leading to the reserve feed tank distilled water from the evaporator-in excess of requirements.

3. A closed feed system for steam power plants as claimed in claim 1, including a connection provided with a iioat-operated valve between the reserve feed tank and one of the condensers. HAROLD HILLIER. 

